Got understeer? Check your tire pressure!

[Jetfire]

For the first time last Sunday, I was able to induce controllable oversteer at an autocross event. The only significant difference in my car's setup was the air pressure - I pumped up the fronts to about 38 psi and left the rears around 33/34. My front end gained an appreciable amount of traction and I was able to let the rear slide out without worrying about losing control. It was an awesome feeling, to say the least. :D

Most experienced autocrossers should know this, and I did too...but I wanted to keep the car as stock as possible for a few events to learn how it handles. Now it's time to experiment.

[TD]

At the last NCC autox, I ran 38F 36R on the S-03s. When I had the Contis, I ran 40F 37R.

But with the staggered tire set up, you pretty much HAVE to run more air up front.

[Jetfire]

Originally posted by TD
At the last NCC autox, I ran 38F 36R on the S-03s. When I had the Contis, I ran 40F 37R.

But with the staggered tire set up, you pretty much HAVE to run more air up front.

Yeah. The only other solution is to get a set of non-staggered wheels. Seriously considering this, but relatively low on my mod list.

[·clyde·]

49 psi up front still gives me a massive amount of rollunder up front, but that's because of my ****ty tires.

WRT managing/dealing with understeer, it bears repeating...slowing down enough before you turn is paramount and something that I had started to forget (and was my big mistake in Bowie). At the council event the day after the last NCC event I purposefully got off the gas and/or braked significantly earlier than I thought I otherwise would. My times compared to the people at both events were much better percentage wise than at the NCC event. I found that very surprising considering that I took the wrong lines through a number of gates and left a lot of time out there on those wrong lines.

You (well, I) think I get this licked, and then I realize how far I still have to go.

[Nick325xiT 5spd]

I ran 40F, 37R at the last autox. I'll probably go to 41F for the final one. :p

I've found that the tires don't really seem to wear unless you're actually getting fairly decent traction. In the autocross before the last one, where I was doing VERY poorly, going WAY too fast into the turns and just generally driving like ****, I had almost no tire wear.

Then I got this. :p

Edit: Naturally, I was still going a fair bit faster into the turns than I probably should have. :p

Right front:
http://www.nrubenstein.com/images/rrburn.jpg

Here's the left front for comparison. My RF looked about like this before the autox. :p
http://www.nrubenstein.com/images/lfburn.jpg

[TD]

Originally posted by Nick325xiT 5spd
I ran 40F, 37R at the last autox. I'll probably go to 41F for the final one. :p

I've found that the tires don't really seem to wear unless you're actually getting fairly decent traction. In the autocross before the last one, where I was doing VERY poorly, going WAY too fast into the turns and just generally driving like ****, I had almost no tire wear.

Then I got this. :p

Edit: Naturally, I was still going a fair bit faster into the turns than I probably should have. :p

Right front:
http://www.nrubenstein.com/images/rrburn.jpg



That's actually about how mine looked as well.

[·clyde·]

Originally posted by Nick325xiT 5spd
Edit: Naturally, I was still going a fair bit faster into the turns than I probably should have. :p

If you were following my lead, you were :(

[nate]

Yea, tire pressures will make a difference. Adjusting pressure is not the ideal way to reduce understeer, more front negative camber is. Too bad you are out of stock.

But, you can't reduce your pressures too much. At the track a few weeks ago, I believe I was running a bit over 40 cold in the rear and was close to rolling off the tread with stock 2 deg negative. Go to high and you will just slide. I need some more front negative camber...

As for auto-x, I haven't driven my car at auto-x for 4 months now. I think that amost all cars now understeer in auto-x. You will find your BMWs much more balanced at higher speeds...

[Nick325xiT 5spd]

Originally posted by Clyde@work


If you were following my lead, you were :(

Heh, it's a concept that so easy to state, but so difficult to fol.low through on. It's just SO hard to make yourself lift/brake earlier. :dunno: :)

[Jetfire]

Here's a great informational page on tire pressure:

http://www.tirerack.com/tires/tiretech/competition/racepres.htm